I took car in for oil change &tune up. 3 visits later my engin blows up.

I took it in for oil change, tune up and a noise I thought might be the front passenger tire. They said there was no problem with tire. They changed oil, did tune up, suggested a fuel cleaning soon. I said I had to go out of town would it still be okay. He said yes. I got 300 miles from home, then the engine light came on. I noticed that the coolant was low in the reservoir tank. After the van cooled,( no lights, etc. indicating it had overheated)I put some water in the reserve tank. Did some internet research and found that by turning key on and off, the computer would give me a code. The code represented a misfire on cylinder 8. I took it back to the place, they said I had a vacuum leak. They did that, the fuel cleanout, and about $600.00 later I get van back. Then about 3 days later, I get 25 miles down the road, and light comes on. Again, coolant low, no overheating, wait a while, engine cranked back up and within a mile of the house noise develops, then suddenly, pop, smoke, and I limp home. Took it to shop, they said I need a used or new engine. Honestly, I never have had a minutes trouble til I took it in to have this place do the oil and tune up.